This invention relates to semiconductor devices and, more particularly, to a method for fabricating photoresponsive semiconductor devices.
Photoresponsive semiconductor devices designed for use in a variety of important practical applications are receiving increasing attention. Thus, for example, considerable effort is being directed to the development of photoresponsive semiconductor devices of the so-called surface-normal type. Illustratively, this class of devices includes asymmetric Fabry-Perot modulators and surface-emitting lasers. For a description of a typical such device, see, for example, "Electroabsorptive Fabry-Perot Reflection Modulators with Asymmetric Mirrors", by R. H. Yan et al, IEEE Photonics Technology Letters, Vol. 1, No. 9, pages 273-275, September 1989.
In contrast with edge-emitting or waveguide-type optical devices, surface-normal optical devices of the type described in the aforecited article lend themselves relatively easily to the formation of two-dimensional arrays. Such arrays are useful in various applications such as optical interconnects, laser printers and smart-pixel systems.
A typical surface-normal optical semiconductor device includes a multi-layer mirror structure on top of which is formed an intrinsic region comprising a multi-layer electroabsorptive region (for a modulator) or an intrinsic region comprising a multi-layer gain region (for a laser). Another mirror is then formed on top of the electroabsorptive or gain region. An optical cavity, exhibiting resonance at a prescribed wavelength, is thereby formed in the device, as is well known in the art.
Multi-layered photoresponsive semiconductor devices, particularly the intrinsic regions thereof, are relatively precise, complex and sensitive structures. Fabricating such devices in a consistent reproducible manner to exhibit specified characteristics is often extremely difficult. In practice, the manufacturing yield of these devices is thus often relatively low. And this is especially true when large arrays of the devices are made in a batch-fabrication process in which uniformity of large numbers of individual complex devices is sought. As a result, the cost of making certain types of photoresponsive semiconductor devices has heretofore been undesirably high.
Hence, it was recognized that a need existed for an improved method for fabricating photoresponsive semiconductor devices. It was apparent that such a method, if available, would have the potential of increasing the quality and uniformity of manufactured devices while improving the yield of the fabrication process and thereby lowering the cost of the devices.